Guide to Stoich

Sarai Alonso

First, what is it?

Stoichiometry, or stoich for short, is the relationship between reactants and products in an equation where it is determined how much product can be made with a certain amount of reactants.

Parts to this guide

  1. Reaction we are working with along with the type of reaction it is, the balanced equation, IUPAC names, and molar masses
  2. Mole to mole conversions
  3. Mass to mass conversions
  4. Limiting and excess reactants
  5. Theoretical yield
  6. Percent yield
  7. Real world aplication

1.) Our Reaction

Lets use the reaction CaO+CO2

This is a synthesis reaction, you can tell because a metal oxide and CO2

come together to form a metal carbonate. carbonate. In this case the metal carbonate CO3.

Balanced Equation: In this case the equation does not need any coefficients (Number in front of an element or compound that is distributed) because it is already balanced meaning there is the same amount of each element on both the reactant and product side

CaO+CO2a Ca(CO3) (aq)

Calcium Carbonate and Carbon dioxide yield Calcium Carbonate


Molar Mass: To find molar mas, take the atomic number of the specific element from the periodic table and if there is a subscript with the element multiply the atomic mass by the subscript. If there is a compound add the individual element masses together.

CaO-56.077

CO2- 44.009

CO3- 108.005

2.) Mole to Mole Conversion

Mole to mole conversion is when there is a given amount of reactants and it is converted into the amount of products that would be made with said amount. To be able to do mole to mole conversion you first have to know the given amount of reactant and the coefficients (found in the balanced equation) in front of the reactant and product. Coefficients are important because they are a ratio between the amount of reactants used and the amount of products made.


To do a mole to mole conversion you will have to use the train track method. Start the with the given amount of reactants and set it up so that you have moles of that same product on the bottom and moles of the product on top. To find out how many moles to calculate with, use the coefficients. Multiply the top numbers and multiply the bottom numbers then divide the top product by the bottom to get your result.

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3.) Mass to Mass

Mass to Mass conversion is when we find out how much the product made will weigh based off of a given mass of a reactant. To do mass to mass conversion you will need: molar masses of the reactants and products (provided in part 1), coefficients (found in the balanced equation), and a starting giving mass of a reactant.


To begin take your given amount and then take the molar mass of that element or compound and set it up, again in the train track method, to equal one mole. Set up the moles of your reactant to the moles of your product and use coefficients to know how many moles of each to calculate with. use the molar mass of the product to have one mole then, multiply the top and bottom separately and divide the product of the top by the product of the bottom

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4.) Limiting and Excess Reactants

In a chemical reaction the reactant that runs out first is called the limiting reactant. The reactant that is more than needed is called the excess reactant. To find which is which you must know: the given amounts of reactants, the molar masses of the products and reactants,and the coefficients in front of the reactants and products.


To find the limiting and excess reactants we will again be using the train track method. We want to convert the given masses of the reactants to moles of the product to see which one makes less product. The one that makes less is your limiting reactant.

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5.) Theoretical Yield

Theoretical yield is the product amount estimated that will be made with the given reactants in moles. To calculate theoretical yield you will have to know the limiting reactant, molar mass of your product, and coefficients.


Begin with your limiting reactants and set the train track so that you have the moles of your reactants with moles of your product. After that convert your moles of your product to grams using the molar mass of your product. multiply the top and multiply the bottom, then divide the top by the bottom and you will get theoretical yield

6.) Percent Yield

Percent yield has to do with the effectiveness of a chemical reaction. The percent yield is always lower than your theoretical yield because there are always other factors that play into a reaction or procedure that cause some of the reactants to be lost or turned into something else so the the 100% theoretical yield is not met. To calculate percent yield you will need to know the actual yield you had and your theoretical yield.


To calculate the percent yield you divide the actual yield by the theoretical yield and multiply by 100.

Real world Application

Typically, the reaction between we used for our example is used in a decomposing way where we start with Ca(CO3) and heat it to break down into CaO and CO2, however; one application of using the reactants in synthesis is in the making of lime stone. Limestone is made of mostly Ca(CO3) and is used make things such as cement
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